A sly grin sneaks across Kyle Wilson’s face. Why do you enjoy covering slot receivers, a job in the Jets defense known as the nickel corner? It is akin to asking an ultramarathon runner why 26.2 miles is not enough.

To elaborate: Why, when blanketing an NFL wide receiver is difficult enough, do you prefer to add another challenging layer by covering often the quickest member of an opposing offense aligned between the offensive line and an outside receiver, in the most chaotic and spacious zone on the field?

Wilson twists a diamond the size of a cherry pit into his left earlobe.

“Because not everyone can do it,” he said. “That’s the thing.”

Those who play in the slot -- the receivers on offense as well as defensive backs -- relish the position and the unique challenges associated with it’s mastery. As Wilson said, the successful are a special subset of NFL players, invaluable to their respective teams and influential over each week’s gameplan. Coaches will stretch their imaginations to find mismatches for strong slot players, and keep their fingers crossed if they have a player in the position who struggles.

A level of comfort and familiarity is required, too. Certain players don’t feel suited, aren’t familiar with the technical tweaks or don’t have the understanding of defensive concepts to adjust to a role coaches say is as much intuitive as rote. It is why Wilson and Jeremy Kerley, the Jets’ slot receiver, are considered indispensable.

“Some guys who play outside and come inside will say, ‘I hate playing the slot.’ It’s just not who they are,” said David Nelson, a Jets wide receiver who caught 61 passes with the Buffalo Bills in 2011 working predominantly in the slot. “They can’t do it because there’s so much weaving in and out and banging off people. And some come off the outside and go inside and realize that’s where they were meant to be all along.”

The ancestors of today’s slot receivers were running backs posted just at the end of the offensive line with an option to sneak out for a pass, block, or loop into the backfield to take a handoff.

When Sid Gillman, the Hall of Fame coach and innovator, overhauled passing philosophy in the 1950s and ‘60s, he fashioned a system where receivers outside and in the slot worked cohesively. The idea is to layer the field with receivers to stretch apart the defense and create space. Through generations of coaches -- Al Davis to Bill Walsh to Steve Mariucci -- the concept trickled into the Jets’ playbook run by Marty Mornhinweg.

“For a slot receiver, it’s everything you could want,” Kerley said. “Our new offense, to me, is made for a slot receiver.”

Kerley stands 5’9, and his 188-pound frame is encased in muscle. He is compact, sturdy and adept at making quick bursts -- or what coaches call “short-area quickness” -- and therefore has played slot receiver since college at Texas Christian University. He has a body type that many slot receivers share.

Mornhinweg uses Kerley, who led the Jets with 56 catches last season and has nine grabs this season in three games, as the underneath layer of a three-tiered system in combination with Stephen Hill and Santonio Holmes, the Jets’ starting receivers on the outside. As Kerley said, when on the field at the same time their routes “finesse each other.”

“You have Stephen who can take the top off, so you’ve got to defend deep,” Kerley said. “Then you’ve got Tone who is a finesse route runner, so he might kill you in between. Then you’ve got me coming underneath. So, where do you want to defend it? You can get beat on all three levels.”

Kerley’s opportunities frequently arrive on third down, when the Jets must pass to reach the sticks and have three wide receivers on the field. Often, Kerley is the primary option for quarterback Geno Smith and so, Jets receivers coach Sanjay Lal said, “there has to be a mentality that I have to win this play.”

Kerley will line up against a linebacker or nickel cornerback. Once the ball is snapped, the player has five yards to shove and bump Kerley, who must stay on course to reach his route’s destination in accord with the timing of Smith’s drop -- a central aspect of Mornhinweg’s system.

“How do I get past that first linebacker or nickel defender in a zone coverage to get into my route?” Lal said. “They’re always dealing with that. Outside, you don’t always deal with that. You get free access. Very rarely does an inside receiver get free access.”

While Holmes and Hill operate near the periphery of the field, where fewer players operate, once in motion, Kerley zips through the murkier middle portion.

Noted Lal, “Things happen faster than way outside, so reaction speed and processing of information has to be faster.”

To anticipate his movements, Kerley will watch film on how the opposition’s nickel cornerback reacts to the routes Kerley will run on gameday and where the defense will try to force him in certain coverages.

“You have to play the game in your mind and in the film room before it happens,” Lal said.

Quick feet and crisp route running are imperative aspects of playing slot, but so is the ability to survey the chaos occurring in the middle of the field and settle into an unoccupied space. The primary goal is to get open. That space, however, evaporates quickly.

Against the Tampa Bay Buccaneers, Kerley dragged across the field, wiggling free of coverage. Mark Barron, the Bucs safety, crashed into Kerley once the ball was caught and knocked his helmet off. Kerley sustained a concussion.

“It’s a little more dangerous in there because there are bigger bodies who are getting paid to hit as opposed to paid to cover,” Nelson said.

Still, Kerley said he prefers playing inside compared to wide, where he will play Monday night in Atlanta in the Jets’ two wide receiver sets because of Holmes’ absence. Kerley said inside, he is too quick for linebackers or safeties to cover -- “That’s our advantage,” Lal said -- and more skilled than nickel defensive backs, often the opponent’s third-best defensive back.

Around the NFL, offenses have reflected Kerley’s sentiment. Of the 10 wide receivers who have been thrown at most this season, seven spend time lined up in the slot.

To combat those receivers, Wilson says a nickel corner must be quick, clever and gritty. Despite some unsteady play this season and shifting in the Jets secondary, Wilson is always on the field when opponents stick a third wide receiver in the slot.

Wilson, of a similar body type to Kerley, has the quickness to stick with slot receivers and a required understanding of how the nickel corner coordinates coverage with the Jets safeties, outside corners, linebackers and sometimes even defensive linemen, Tim McDonald, Wilson’s position coach, said.

The challenge comes in working in the middle of the field, where the barrier of the sideline can’t be used as an aid. A receiver, Wilson said, has a “three-way go,” he can head left, right or vertical. The routes happen closer to the quarterback, so throws arrive more quickly.

“You’ll see guys who play one position, see what happens when you put them in the middle of the field,” Wilson said. “Guys who aren’t used to that position, you get your hips turned the wrong way a little bit and a lot wrong can happen."